There were cheers and squeals and fluttered flags, sustained and perhaps a little pointed, as Zhang Yufei walked out for the women’s 100m butterfly semi-final at 8.38pm inside the agreeably boisterous La Defénse Arena.

Zhang waved and smiled, always looking straight ahead, then reeled off a 56.15sec race to take second place and book a spot in the final. All Olympic athletes need to find that neutral space, to close out the noise, to create a kind of light around themselves. In Zhang’s case, as with 10 other Chinese swimmers in Paris, this will involve a note of additional defiance at a competition already charged with its own note of wider tension.

It was always going to be a vivid first day in the pool, with a painfully sharp note of contrast to the two major stories of the day. On the one hand Paris 2024 dished up the pure sport of the women’s 400m freestyle final, billed in advance as Race of the Century fodder.

This was elite stuff, with Ariarne Titmus, the reigning champion, leading from the start to take it home ahead of Katie Ledecky, perhaps the greatest female swimmer of all time; and in the silver medal spot the brilliant Canadian teenager Summer McIntosh, an athlete so on point with these rain-sodden Games she is even named after Paris 2024’s current must-have garment. We all need a summer Mackintosh right now.

Simultaneously Paris 2024 found itself the unwitting host for the other race of the century: a familiar cold war that is not just the opposite of sport, but the thing that might come closest to killing it.

From the moment the story first broke in April that 23 Chinese swimmers had been cleared of a previously unpublicised doping offence before the Tokyo Olympics, these Games were always going to signal a reopening of a familiar background hum. Suspicion, distrust, doubt, accusations: these are toxic elements in their own right. With UK Anti-Doping (Ukad) facing questions of its own on that front, it is above all the process that stands out here.

The World Anti-Doping Agency (Wada) has been very clear that it is entirely happy, as rubber-stamped by an independent report, with its findings in this case. The Chinese swimmers had tested positive for TMZ, a performance-enhancing heart drug. Nothing was made public at the time. The case was first publicised by the German TV station ARD and the New York Times, by which point many of those listed as affected had competed at Tokyo 2020. Eleven of those named in the reports are competing in Paris.

And this was the nub of the opening day at La Défense, where three of the Chinese swimmers cleared by Wada were in the pool. First up was Zhang Yufei. Fei Lewei went in the men’s 400m freestyle final. Qin Haiyang, a combative defender this week of China’s doping record, swam in the men’s 100m breaststroke semi-final and will now be relishing the chance to race for gold against Adam Peaty.

Earlier in the day Peaty had spoken pointedly about not wanting “any cheats in the pool”, referring in that moment to technical rulings by the swimming version of football’s video assistant referee. But the tension around this issue is very real. It was present here, with a sense of not just of competitive rivalries, but of wider opposition, cultural strain.

Swimming is a natural repository for this kind of friction. It is in the nature of the sport, a micro-test of technique and wing power and endless repetitions, but one that is uniquely receptive, in theory, to the benefits of doping. This is a discipline that is all about training overload, resistance, the endurance of agonies, pain that happens out of sight.

As such it has been more vulnerable than most to the question that lies behind these rules in the first place. Do we trust the spectacle? Is this real? Because it all falls apart if not. And this is why the handling of the Chinese case drew concerns.

At the time Wada accepted the case of China’s own doping agency that its swimmers had stayed at a Huayang Holiday hotel in Shijiazhuang where traces of TMZ were also later found in the kitchen drains and on counter tops. From there that this must have also been how the drug got – presumably – into the athletes’ food. Exactly why TMZ would be down drains and on kitchen counters was never made clear. Perhaps a coach-load of heart patients were also in town for a conference?

Some have argued that the doses found were too small to be significant, which seems irrelevant, but also the very heart of the issue. Without zero tolerance, with carve‑outs and caveats, doping policy basically falls apart. The suspicion will inevitably remain, among those who doubt the process, that Wada has failed to challenge adequately the evidence presented, that perhaps China is simply too big to tangle with on this.

Saturday was the first day of major competition since this all came to light. And of course the fallout is already toxic. This past week Qin posted a feisty social media message claiming the increased drug testing of Chinese swimmers was a tactic designed to throw his country’s athletes off their stride.

China has often suggested this is all a result of Sinophobia, racism, US propaganda. There is even a theory China now welcomes, at an obscure political level, the suspicions around its athletes, which is presented as evidence of hostility, a unifying sense of national victimhood.

At which point, before anyone gets too righteous around here, before we start to wonder why the rest of the world can’t live up to the rigorous standards of UK Anti‑Doping, it is worth considering the recent case of Jade Jones.

Chinese media certainly will when the taekwondo begins in the second week of the Games, with Jones, a two-time gold medallist, ready to go for the three-peat. The story of Jones’s missed drug test got a little lost in the climax to Euro 2024. It goes like this.

In December a doping control officer came to her hotel in Manchester at 6.50am and asked for a urine sample, which was refused. Refusing a test can result in a four‑year ban. Instead Jones received no punishment and is competing in Paris after her mitigation was accepted on appeal.

Jones submitted via her lawyer that she was so dehydrated from trying to make weight to compete that her cognitive abilities were seriously affected, to the extent she could no longer make rational choices. She tested negative 12 hours later, a short but still significance interlude. A investigation later found that she “bore no fault or negligence for her refusal to submit to sample collection”.

This week Mark England, Team GB’s chef de mission, insisted he was “completely comfortable” with the whole process, pointed out that Jones had been double-exonerated by Ukad and Wada, and made mention of her own “remorse”, which is fine but also completely irrelevant.

Exactly why anyone could feel comfortable about this isn’t clear. Ukad is, in the end, a government body. How does this look? How is the UK supposed to claim any greater authority on these issues when the idea of zero tolerance, of living the code, of no exceptions starts to fray at the edges? Ukad was even part of the review and clean up operation after Russia’s state‑sponsored doping programme was exposed. What will they make of this in Russia?

Credibility is a fragile thing. The spectacle is fragile. La Défense served up some beautifully pure moments on Saturday night, not least a brilliant women’s 4x100m relay final, won by a beaming Australian four ahead of the US and China. But it also opened the book here on the race behind the race, a return of doubt and opacity and bodged processes, and a backstory that might just find its own voice in the days to come.